Download Delay-free audio coding based on ADPCM and error feedback Real-time bidirectional audio applications, like microphones and monitor speakers in live performances, typically require communication systems with minimum latency. When digital transmission with limited bit rate is desired, this poses tight constraints on the algorithmic delay of the audio coding scheme. We present a delay-free approach employing adaptive differential pulse code modulation (ADPCM) and adaptive spectral shaping of the coding noise. To achieve zero-delay operation, both prediction and quantization logic of the ADPCM structure are realized in a backwardadaptive fashion. Noise shaping is accomplished via two feedback loops around the quantizer for efficient exploitation of the auditory selectivity and masking phenomena, respectively. Due to automatic optimization of the involved parameters, the performance of the proposed system is on par with that of prior low-delay approaches.
Download On the Use of Sums of Sines in the Design of Signal Windows Windowing of discrete signals by temporal weighting is an essential tool for spectral analysis and processing to reduce bias effects. Many popular weighting functions (e. g. Hann, Hamming, Blackman) are based on a sum of scaled cosines. This paper presents an alternative class of windows, constructed using sums of sines and exhibiting unique spectral behavior with regard to zero location and a side lobe decay of at least –12 dB/octave due to guaranteed continuity of the weighting. The parameters for the 2- and 3-term realizations with minimum peak side lobe level are provided. Usage of the sum-of-sines windows with the DFT and their adoption to lapped transforms such as the MDCT are also examined.